Research On Foam Inhibition Mechanism During Viscous Oil Delayed Coking Process And Antifoams Developing

When a delayed coking unit is used to handle viscous oils, high foam layer often forms incoke drum, which has become one of the bottlenecks that affect safe and stable operation of thecoking unit. A lot of work had been done for viscous oil coking to obtain the foaming tendency,uncover the foam layer formation mechanism, figure out the mechanism of action of someantifoaming measures, and develop efficient antifoams. In this study, the foaming performanceof different viscous oil under non-reaction and thermal reaction conditions were determined bythe self-designed heavy oil coking foaming performance evaluation apparatus. The influenceof the factors such as composition of heavy oil, reaction temperature, and viscosity of heavy oilat high temperature on the foaming performance of viscous oil under coking conditions wasstudied. The effect of recycle oil and recycle ratio on the foaming performance of viscous oilduring the coking process with coking distillates recycling was investigated. High efficientantifoams, which were able to suppress the foaming performance of heavy oil under cokingconditions effectively, were developed by the method of formulating and modifying. And thecorresponding antifoaming mechanism of the antifoams was studied. The results are as follows:In cold simulating experiments, there was an obvious correlation between the foamingperformance and resin content of feedstocks, while there was no obvious correlation betweenthe foaming performance and asphaltene content apparently. Results of further study showedthat resin must be the main factor that determines the viscosity of foaming system, whileasphaltene must be the main factor affecting the surface properties. The foaming performanceevaluation results from thermal simulation were almost consistent with that from coldsimulation, which indicated that the viscous oil with strong foaming nature usually showedstrong foamability during coking process. And with reaction temperature increasing, the highestfoaming height of the same viscous oil decreased, which accorded with the operation experience from real delayed coking process. The viscosity of viscous oil at the temperature under whichthermal reaction was about to start also had an effect on the foaming performance at thermalsimulating experiments. High viscosity at350℃often lead to high average foaming height.Nucleation of gas bubbles was the main mechanism of foam layer formation in delayed cokers.Coking distillates recycling had a suppressive effect on heavy oil foaming performanceduring coking process. Lighter recycle oil and higher recycle ratio would lead to a betterantifoaming performance. The reason was that using light recycle oil and increasing recycleratio both contributed to the decrease of viscosity and polar molecules concentration infeedstock.The high efficient antifoams selected by cold simulation were the antifoams formulatedwith B+n-heptanol (6/4) and A+isooctanol (6/4). These two antifoams were able to lower theaverage foaming height in thermal simulation effectively. Bridging-stretching mechanism wasthe main action mechanism for the antifoams.